As the present invention is directed to apparatus and methods for treatment of patellofemoral conditions, a basic discussion of the anatomy of the knee with a focus on the patellofemoral structures may assist in describing the various embodiments of the invention. FIG. 1 is a schematic portrayal in side view of a human knee. The bones of the knee joint comprise the femur (F), tibia (T), and patella (P). The fibula (fib) is another bone in the lower leg that attaches to the tibia. As primarily relevant to embodiments of the present invention, connective tissues of the knee joint include the patellar tendon (PT) and the quadriceps tendon (QT). The patellar tendon is also referred to as the patellar ligament as its primary function is to create a connection between bones, i.e., the tibia and patella. The patellar tendon extends from the caudal (lower) extent of the patella to an attachment point on the tibial tuberosity (TT) of the tibia. The tibial tuberosity comprises a raised area on the anterior (forward) aspect of the tibia, caudally positioned (toward the foot or lower) with respect to the cranial (upper) end of the tibia. The quadriceps tendon extends from the cranial extent of the patella and joins with the quadriceps-femoris muscle.
The knee is a synovial joint, meaning that the bones are not directly joined but are surrounded by dense connective tissues forming an articular capsule (C) lined by a synovial membrane. The capsule defines a synovial cavity or intracapsular space (IC) that contains the articular cartilage of the joint (not shown) and synovial fluid that acts to reduce friction between the articular cartilages. The approximate extent of the capsule is indicated in FIG. 1 by dashed lines (C′). The quadriceps and patellar tendons lie outside the capsule. Also outside the capsule is the infrapatellar fat pad (FP). The fat pad is situated posteriorly and caudally with respect to the patella and joins with the patellar tendon on its posterior side over much of its length. The knee joint also includes a number of bursae to protect and facilitate movement between various bony and soft tissues. One of these bursae is the deep infrapatellar bursa (B), which allows for movement of the patellar tendon over the tibia. This bursa is positioned between the upper part of the tibia and the patellar tendon and lies in a pocket outside of the infrapatellar fat pad.
Because of the importance of the capsule in protecting and lubricating the articular cartilage, it is usually preferable, whenever possible in a knee intervention, to avoid penetrating the capsule. Because of the role of the infrapatellar fat pad in protecting the knee, it is also usually preferable to avoid dissecting the fat pad during knee interventions. Previously, removal of all or part of the fat pad was common in arthroscopic procedures in order to permit better visibility for the surgeon. However, it has been discovered that damage to the fat pad can lead to scarring, which can be painful and even crippling in some patients.
Treatments for various patellofemoral pathologies such as patellofemoral pain and patellofemoral osteoarthritis (PFOA) have been increasingly investigated. One early treatment, which involves anteriorization of the patellar tendon by a relatively invasive surgical procedure, was devised by Dr. Paul Maquet in the early 1960s. See, P. Maquet, 30 Revue Du Rhumatisme, No. 12, December 1963, pp. 779-783, “Biomechanical Treatment of Patellofemoral Osteoarthritis, Advancement of the Patellar Tendon” (translated title). In this procedure, an iliac bone autograft is implanted under the patellar tendon to relieve pressure in the patellofemoral space. Later Dr. Maquet evolved his technique to cut the tibial tuberosity away from the tibia and reposition it. This became known as the Maquet Osteotomy, which has been performed on tens of thousands of patients over the years with positive results. See, e.g, Maquet, Biomechanics of the Knee, pp. 134-143 (pub. Springer-Verlag 1976). However, the Maquet Osteotomy is a highly invasive procedure, which carries with it all of the risks and costs associated with highly invasive orthopedic surgeries.
FIG. 2 is a schematic illustration of a relatively square bone implant 2 of the type proposed by Dr. Maquet implanted on the tibia (T) under the patellar tendon (PT). The patellar tendon is attached cranially to a caudal portion of the patella, and caudally to the tibia at the Tibial Tuberosity (TT). The natural line of action of the patella tendon would be generally along a line (L) extending between the two attachment points. Placing the bone implant 2 under the patellar tendon moves the patellar tendon anteriorly between its two attachment points and thus alters the line of action with respect to the patella. The new line of action (L1), oriented more away from the patellofemoral space can reduce the pressure on that space. Said another way, anteriorizing the patellar tendon renders the angle between the patellar tendon and the quadriceps tendon more obtuse, reducing the resultant force pressing the patella against the femur.
However, the success of such a procedure may depend heavily on the configuration of the implant used. If the anterior, tissue-engaging surface of the implant is roughly perpendicular to the caudal face of the implant and/or parallel to the underlying surface of the tibia, it displaces the patellar tendon relatively directly anteriorly (perpendicular to the tibial surface) and creates an abrupt step at the caudal edge of the implant, which can produce a number of complications. First is the creation of an unsightly bump on the knee. This is not merely a cosmetic problem, as the bump may catch on clothing or other, harder objects that could cause bruising or injury in the course of daily activity. Second, such an implant could be extremely uncomfortable in certain common positions. For example, if a patient with such an implant were to kneel on that knee, all of the load would be placed on that implant, which could be painful and also damaging to the patellar tendon.
A third possible complication arises from the fact that an implant shaped such as implant 2 also pulls the patella caudally, creating an undesirable misalignment. This condition is referred to as “Patella Infera” or “Patella Baja”. The symptoms of this misalignment can include pain on quadriceps contraction, inadequate quadriceps contraction, swelling, edema, joint stiffness, limited joint motion and limited patellar mobility.
Further, it may be desirable to maximize the area of the posterior surface of the implant that lies against the bone in order to spread the forces on the implant over as wide an area as possible. And, in order to minimize Patella Baja, it may be desirable to engage the patellar tendon as far cranially as possible without interfering with the patella or other tissues during knee movement. Yet, the space in which the implant is to be located, between the tibial tuberosity and the fat pad, bursa, and/or capsular tissues, is extremely limited. If the posterior surface of the implant extends too far cranially along the bone surface it may interfere with the fat pad, bursa, or joint capsule, causing pain or other complications. What is needed, therefore, are devices and methods for relieving patella-femoral pain due to osteoarthritis or other conditions that overcome the foregoing challenges.